The present invention relates to an apparatus and method of selectively generating charged particles in which one of or both of ions and electrons are generated.
In the conventional ion source having a needle electrode, a vacuum (e.g., about 10−8 Pa) was created around the needle electrode. A gaseous raw material was supplied to the tip end of the needle electrode at room temperature. Thus, the vacuum around the needle electrode was reduced to about 10−2 Pa. The needle electrode was cooled depending on the type of ion to be generated. The gaseous raw material was liquefied and ionized by a strong electric field between the needle electrode and an extract electrode. Thus, a cooling device for liquefying the raw material was essential in the prior art. Moreover, the prior art wasted the supplied raw material since it most flowed into the vacuum/exhaust system.
In recent years, there is a large demand for a single device for emitting both the electron and ion beams in the field of nanotechnology. For example, drawing or machining will be carried out by selectively using the property of electron or ion beam. Alternatively, a drawing or ion-injecting process using the ion beam may be monitored by the electron beam.
In the latter case, an electron may be emitted from the needle electrode after the supply of raw material from the ion source has stopped. Since the raw material has adhered on the tip end of the needle electrode, however, it is required that any heating mechanism is used to remove the adhered substances and to emit an electron from the clean face of the needle electrode.
In such a manner, when the needle electrode is used as an ion source, it is cooled. When the needle electrode is used as an electron source, it is heated. As a result, the temperature of the needle electrode must rapidly be changed, for example, within a range around several K to 200 K. This requires any cooling device such as a tank containing liquid helium or nitrogen or any refrigerator, as well as any heating device.
The atmospheric pressure around the needle electrode is 10−8 Pa when it is used as an electron source. When the needle electrode is used as an ion source, the pressure around the needle electrode may be, for example, about 10−2 Pa depending on the gaseous raw material. To realize such different pressures in a rapid manner, a turbo-molecular pump (or oil diffusion pump) resistible any increased load is required. In addition, difficulties in operation and higher cost are unavoidable for such of differential pumping system.